Method for sink and float separation of fine grained mineral raw materials

ABSTRACT

A separating apparatus for the sink and float separation of a mineral raw material according to density using a liquid. The separating apparatus includes a rotatable drum including a plurality of sink-product pockets for discharging a sink product of the mineral raw material. The apparatus also includes a raw material inlet for delivering the raw material into the liquid bath, a first liquid inlet and first liquid outlet including an overflow disposed at a top level of the liquid bath, and a second liquid inlet and second liquid outlet. The separating apparatus also includes a front deflecting barrier and a rear deflecting barrier, each projecting into the liquid bath from above and disposed over an entire width of the liquid bath. In addition, a method for the sink and float separation according to density of a mineral raw material using a liquid.

The present invention relates to an apparatus for the sink-and-floatseparation of mineral raw materials and to a method for thesink-and-float separation of mineral raw materials.

For the processing of mineral raw materials and their separation fromundesirable accompanying constituents, for example for the separation ofthe debris constituents contained in raw coal and the clean coal,various separating methods are known which separate the variousconstituents of the raw material on the basis of their differentspecific weights, for example dynamic methods such as cylinders orcyclones, in which dense medium rotates and forms a vortex, or jigs, butalso static methods with washing drums (sink-and-float separatingapparatuses). For the processing of fine-grained mineral mixtures, inparticular raw coal fractions as well, for example smaller than 12 mm,virtually only dynamic separating methods with cylinder or cyclone weresuitable hitherto if a high separation grade was required, but saiddynamic separating methods have the disadvantage of a low delivery andthroughput capacity with high specific consumption of energy and pulpthroughput. Although it was possible to achieve higher capacities withjigs and sink-and-float separation apparatuses, the separation grade tobe achieved with these apparatuses and corresponding methods wasinadequate.

This situation is explained by the table below, in which technicalclassification figures of some separating methods for coal are compared.In this case, the DWP cylinder represents cylinders and the DSM cyclonerepresents cyclones, and the washing drum represents a sink-and-floatseparating apparatus, the values specified applying to the processing ofa grain fraction of 3 to 12 mm with cylinder and cyclone and of coarsecoal with the washing drum. The values for the processing of the grainfraction of 3 to 12 mm with the washing drum would be considerablypoorer. The characteristic figure according to Terra E_(T), which wasdetermined from the partition curve according to Tromp, was selected asa measure of the separation grade. In this case, the E_(T) values of0.04 for cylinder and cyclone are nearer to theoretical target valueswhich can scarcely be reached in practice.

Method DWP cylinder DSM cyclone Washing drum Grain size −3 to 12 mm-Coarse coal Size Ø 400 mm Ø 600 mm Bath 1780 mm Material m³/h  35  80140 delivery E_(T) 0.04–0.07 0.04–0.07  0.09 Pulp m³/h 170 450 220quantity m³/t/h  6.3  7.5  2.2 Pumping kW  37.5  75  37.5 capacity

Apparatuses and methods described at the beginning have been disclosedby DE 11 93 892 and DE 33 27 040.

Apparatuses and methods described at the beginning have also beendisclosed by DE 968 121, the apparatus additionally having a secondinlet and outlet pair for the liquid below the liquid level. In themethod described therein, the bottom liquid flow is so strong that itdrives heavy material into the region of the scoop feeders, arrangedlaterally on the end face of the drum, for thesink-product/heavy-material discharge and acts as a transport flow forheavy material. In this case, float product adhering to the heavymaterial may be discharged with the sink product, as a result of whichthe yield drops.

SUMMARY OF THE INVENTION

The present invention is based on the technical problem of developing anapparatus with which mineral raw materials, in particular coal ofsmall-grained fractions, can be separated according to density fromundesirable accompanying constituents and with which a high separationgrade and capacity can be achieved with a low specific consumption ofenergy and throughput of operating media, and to propose a method withwhich this object can be achieved.

With the apparatus proposed, it is possible to build up a dense-mediumbath with a steady, uniform flow from the inlet side of the separatingvessel to the outlet or overflow side. In order to avoid disturbingeffects on the uniform flow, the discharge drum is only rotated slowly.In particular, care is also to be taken to ensure that the same pulpquantities are fed and discharged at the bottom inlet and outlet so thatthe flow runs horizontally and no vertical flows are superimposed.

With the apparatus proposed, with values which were otherwise the sameas with the conventional washing drum for coarse coal, it was possibleto process a grain fraction of 3 to 12 mm with an E_(T) of 0.02 and thusa very good separation grade. It was even possible, although with halfthe feed quantity of 70 m³/h, to separate a coal grain fraction of 1 to3 mm having a very clean end product, which indicates a high degree ofseparation.

The deflecting barriers proposed in a special embodiment cause the floatproduct floating at the surface to plunge into the dense-medium bath, asa result of which the grains perform a movement relative to the densemedium and in the process are separated from sink-grain fractionspossibly still adhering or from enclosed sink-grain fractions, so thatone can subsequently float up again in separated form. The reardeflecting barrier in the direction of flow has the advantage that itdivides the float-product layer and reduces the thickness of thefloat-product layer, as a result of which the heavy material isliberated from the surrounding float product and can sink unhindered.The course of the bottom edge of the deflecting barrier parallel to andjust below the liquid level has the advantage that the dense-medium flowis deflected in a way that does not disturb the uniform and essentiallylaminar flow.

In a preferred embodiment, the plate of the rear deflecting barrier inthe direction of flow has corrugations arranged parallel to one another,so that on the bottom of the corrugation profile only relatively smallfloat-product layers form, which with their small surface size,influence and decelerate the flow to only a minimum extent. Thecorrugations may have both a rounded-off profile and a V-shaped profile.The height of the arrangement of the rear deflecting barrier isadvantageously empirically set in such a way that a desired fraction ofthe float product is caught by the deflecting barrier and forceddownward into the bath. An expedient control variable for the fractionto be caught is the separation grade of the separated material, which isexpediently to be determined at the overflow.

In a special embodiment, the top inflow line for the dense mediumextends over the entire bath width. An essential precondition for theformation of a uniform flow over the entire bath width is thus provided.This can be arranged in an especially advantageous manner if the inletdevice permits the control of the flow profile over its width. This ispossible, for example, by an inlet device which consists of a vesselextending over the bath width and having at least one inlet opening and,toward the separating vessel, a multiplicity of equispaced openings, thecross section of which can be specifically reduced from inside. This maybe effected, for example, by screens which are arranged inside thevessel and can be operated from outside and with which the free crosssections of the individual outlet openings can be specifically covered,as a result of which the discharging liquid flow is reduced. With suchan apparatus, discontinuities or disturbances of the flow which areobserved during operation can be specifically countered.

In a further special embodiment, the apparatus, for the delivery of theraw material to be separated, has a chute which is inclined towards theseparating vessel and which has a plate which is arranged on the baseand consists of a profiled material corrugated in the longitudinaldirection, the end of this chute being arranged at an adjustabledistance above the liquid bath. The inclination of the chute and thearrangement of its end above the liquid bath causes the raw material tobe delivered onto the liquid bath, at a speed adjustable by theinclination, and to plunge into said liquid bath. The corrugated designof the chute base leads to a reduction in the frictional resistance andthus in the braking effect of the base layer. The spraying of the feedmaterial with water assists the discharge of the raw material from thechute and dilutes the dense medium in the region of the raw-materialdelivery, thereby favouring the heavy-material constituents to sink. Itis also important that the first deflecting barrier is arranged in sucha way that it lies downstream of the trajectory parabola of the feedmaterial, so that the latter does not hit the deflecting barrier, afactor which would lead to a reduction in the feed rate and thus to areduction in the depth to which the raw material plunges into thedense-medium bath.

The uniform distribution of a large number of sink-product pockets overthe circumference of the drum shell causes the sink product to becorrespondingly distributed over the various sink-product pockets andensures that the pockets are not filled unevenly or to an excessivedegree. The liquid-permeable design of the walls of the sink-productpockets, together with the small extent the pockets are filled with thesink product, ensures that no liquid is skimmed off when a sink-productpocket is lifted out of the liquid bath and that the liquid level is notgreatly affected by the only slight displacement volume of the pocketcontents.

The formation of two horizontal liquid flows has the advantage that thefloat product is conveyed to the overflow with the top liquid flow, andthe sink product is caught by the flow at two different bath heights andis moved relative to the dense medium, whereby the separated heavymaterial can sink and adhering float product can be released and canfloat up. The extent to which the heavy material is caught by the flowis increased by the flow deflection. The delivery of the raw material athigh speed to the liquid bath and the deep plunging of the sink-pproduct fractions caused thereby favours the separation of theheavy-material fractions from adhering float-product grains, which isalso intensified by the spraying of the raw material with water and bythe resulting dilution of the dense medium in the region of theraw-material delivery.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages of the invention are explained in the description of anexemplary embodiment, which is shown in the attached drawing, in which:

FIG. 1 shows a partly sectioned sink-and-float separating apparatus inperspective representation, and

FIG. 2 shows the front view of a sectioned apparatus according to FIG. 1during operation.

DETAILED DESCRIPTION

A partly sectioned sink-and-float separating apparatus is shown inperspective representation in FIG. 1. In the trough-shaped separatingvessel 1, the drum 2 is rotatably arranged. The drum is driven by fourvertically adjustable gears (not shown) by means of a centrally arrangedpinion (likewise not shown) engaging in the toothed rim. Thesink-product pockets 3 distributed over the inner circumference of thedrum shell can be clearly seen, their walls being designed to bepermeable to liquid. When the sink-product pockets are rotated into atop position, the sink product discharged into the sink-product pocketsfalls downward by gravitational force into a sink-product chute 4, bymeans of which the sink product is brought out of the separating vessel.In order to prevent the sink product from falling back onto the pulpbath or onto the float product floating thereon, cover plates 5 arearranged in the top area. The raw material to be separated is deliveredvia the delivery chute 6, which has a corrugated base 7. The frontdeflecting barrier 8, which in the exemplary embodiment shown has theform of an angled plate, and the rear deflecting barrier 9, whichconsists of a corrugated plate arranged transversely to the direction offlow and, like the front deflecting barrier, extends over the entirebath width, can readily be seen. The top pulp inlet 10 and the overflowweir 13 arranged opposite at the same height can clearly be seen. Thebottom pulp inlet 11 and, opposite it, the outlet opening 12 of thebottom pulp outlet can clearly be seen just above the sink-productpockets 3. The pulp-bath boundary plate 14, to which the one end of therear deflecting barrier 9 is fastened, is shown in the top rear region.

The front view of a sectioned apparatus during operation is shown inFIG. 2. Via the delivery chute 6 having the corrugated base 7, the rawmaterial is delivered from the right at high speed by the inclination ofthe chute 6, if possible without retardation, onto the dense-medium bathin such a way that it plunges into the bath. Approximately at the heightof the pulp bath, fresh pulp is fed on the right-hand side via the toppulp inlet 10, whereas arranged opposite it at the same height is theoverflow weir 13, via which the horizontal flow of float product isdischarged, with corresponding pulp quantities also flowing off. Whilethe sink-product fraction sinks down through the pulp bath, the floatproduct is conveyed to the overflow weir by the horizontal dense-mediumflow. The pulp flow is deflected by the front deflecting barrierplunging into the pulp bath and by the rear deflecting barrier 9arranged approximately in the center between inlet 10 and overflow weir13. The float-product fractions floating at the top are forced downwardinto the bath by the deflection of the pulp flow, as a result of whichthe separation of sink-product fractions from adhering float-productfractions is intensified and the separating effect is favorablyinfluenced overall. The sinking heavy material falls into thesink-product pockets 3 distributed over the circumference and isconveyed upward by the rotation of the drum and discharged. Afterappropriate rotation of the drum, the sink product falls onto thesink-product chute 4, via which the sink product is discharged from theseparating apparatus.

The bottom pulp inlet 11 and the outlet opening, arranged opposite it atthe same height, of the bottom pulp outlet 12 can readily be seen inthis representation. The sinking heavy material is caught by thehorizontal pulp flow formed between the pulp inlet and the pulp outletand is moved once again relative to the dense medium, which promotesfurther separation of the sink-product fractions from adheringfloat-product fractions. After this second separating stage, the floatproduct rises again in order to be combined with the top pulp flow anddischarged toward the overflow weir 13. The cover plates 5 arranged inthe top rear region and the pulp-bath boundary plates 14 can also beclearly seen.

LIST OF DESIGNATIONS

-   1 Separating vessel (trough)-   2 Drum-   3 Sink-product pockets-   4 Sink-product chute-   5 Cover plates-   6 Delivery chute-   7 Corrugated base-   8 Front deflecting barrier-   9 Rear deflecting barrier-   10 Top pulp inlet-   11 Bottom pulp inlet-   12 Outlet opening of bottom pulp outlet-   13 Overflow weir-   14 Pulp-bath boundary plates

1. A separating apparatus for the sink-and-float separation according todensity of a mineral raw material using a liquid, the separatingapparatus comprising; a drum rotatable about a drum axis for holding aquantity of the liquid as a liquid bath, the drum including a pluralityof sink-product pockets disposed on an inner circumference of the drumfor discharging a sink product of the mineral raw material; a rawmaterial inlet for delivering the raw material into the liquid bath; afirst liquid inlet disposed at a top level of the liquid bath; a firstliquid outlet opposite the first liquid inlet and at the top level ofthe liquid bath, the first liquid outlet including an overflow forseparating a float product of the raw material; a second liquid inlet; asecond liquid outlet disposed opposite the second liquid inlet and at asame height as the second liquid inlet, each of the raw material inlet,first and second liquid inlets and first and second liquid outlets beingarranged parallel to the drum axis, a front deflecting barrier; and arear deflecting barrier, wherein each of the front and rear deflectingbarriers project into the liquid bath from above and are disposed overan entire width of the liquid bath transversely to a flow direction ofthe liquid, and wherein the front deflecting barrier is disposed justbehind the raw material inlet in the flow direction and the reardeflecting barrier is arranged at an approximate center between thefirst liquid inlet and the first liquid outlet so as to divide a layerof the float product.
 2. The separating apparatus as recited in claim 1,wherein the raw material includes coal and wherein the liquid includes adense medium.
 3. The separating apparatus as recited in claim 1, whereinthe second inlet and the second outlet are disposed just above a heightof a lowermost set of the plurality of sink-product pockets.
 4. Theseparating apparatus as recited in claim 1, wherein the raw materialinlet delivers the raw material into the liquid bath in a trajectoryparabola and wherein the front barrier is disposed downstream of thetrajectory parabola.
 5. The separating apparatus as recited in claim 4,wherein the front barrier includes a plate angled transversely to theflow direction and a bottom leg directed obliquely downward in the flowdirection, a bottom edge of the bottom leg being arranged parallel toand just below the top level of the liquid bath.
 6. The separatingapparatus as recited in claim 1, wherein the rear barrier includes acorrugated plate having a leading edge, a trailing edge, andcorrugations disposed parallel to one another in the flow direction, thecorrugated plate being arranged obliquely such that the leading edgelies approximately parallel to and at a height of the top level of theliquid bath and the trailing edge lies below the leading edge.
 7. Theseparating apparatus as recited in claim 6, wherein the corrugationshave a rounded profile.
 8. The separating apparatus as recited in claim6, wherein the corrugations have a V-shaped profile.
 9. The separatingapparatus as recited in claim 1, wherein the first liquid inlet extendsover an entire width of the liquid bath.
 10. The separating apparatus asrecited in claim 9, wherein the first liquid inlet permits a controlledflow profile over an entire width of the first liquid inlet.
 11. Theseparating apparatus as recited in claim 10, wherein the first liquidinlet includes a vessel extending over the width of the liquid bath, thevessel having at least one inlet opening and a multiplicity of equallyspaced outlet openings to the drum, the outlet openings each having areducible cross-section.
 12. The separating apparatus as recited inclaim 1, wherein the raw material inlet includes a delivery chutedisposed at an incline toward the drum, a base of the chute including alongitudinally corrugated profile, a distance between an end of the baseand the top level of the liquid being adjustable.
 13. The separatingapparatus as recited in claim 12, further comprising a spraying devicedisposed above the delivery chute for spraying the raw material withwater in the direction of the drum.
 14. The separating apparatus asrecited in claim 1, wherein the plurality of sink-product pocketsincludes a multitude of sink-product pockets distributed uniformly overthe circumference.
 15. The separating apparatus as recited in claim 4,wherein the walls of the sink-product pockets are permeable to theliquid.
 16. A method for the sink-and-float separation according todensity of a mineral raw material using a liquid, the method comprising:feeding a first portion of the liquid through a first liquid inlet intoa rotatable drum of a separating vessel and discharging the liquidthrough a first liquid outlet disposed directly opposite of the firstliquid inlet so as to form a first horizontal flow in a liquid bath inthe drum, the first liquid inlet and the first liquid outlet beingdisposed at and just below the top level of the liquid bath, the drumhaving a plurality of sink-product pockets distributed over an innercircumference of the drum; feeding a second portion of the liquidthrough a second liquid inlet into the rotatable drum and dischargingthe liquid through a second liquid outlet disposed directly opposite thesecond liquid inlet so as to form a second horizontal flow in the liquidbath, the second liquid inlet and the second liquid outlet beingdisposed at a height just above a lowermost set of the plurality ofsink-product pockets, the first and second horizontal flows beinguniform, essentially laminar, and parallel to an axis of rotation of thedrum; delivering the raw material in a direction substantially parallelto the liquid so that the raw material is plunged into the liquid bathat an inlet side of the drum; separating a float product of the rawmaterial on a side of the drum opposite the inlet side using anoverflow, a sink product of the raw material sinking through the liquidbath; and deflecting a first horizontal flow using a front barrier and arear barrier, each disposed transversely to a direction of liquid flow,the front and rear barriers projecting into the liquid bath from above,the front barrier being disposed directly downstream of the first inletand the rear barrier being disposed approximately centrally between thefirst inlet and the first outlet.
 17. The method as recited in claim 16,further comprising uniformly regulating the first horizontal flow over awidth of the bath.
 18. The method as recited in claim 16, wherein thedelivering is performed at high speed.
 19. The method as recited inclaim 16, wherein the second horizontal flow moves the sink productrelative to the liquid and releases float-product fractions adhering tothe sink product, so that the float-product fractions can rise into aregion of the first horizontal flow.
 20. The method as recited in claim16, further comprising dividing a float-product layer using the rearbarrier and reducing a thickness of the float-product layer.
 21. Themethod as recited in claim 16, wherein the deflecting is performed so asto catch a predeterminable fraction of the raw material floating on asurface of the bath and forcing the predeterminable fraction into theliquid.
 22. The method as recited in claim 16, further comprising atleast one of spraying and water jetting the raw material.